The invention relates to die casting or injection molding apparatus, and, more particularly, to apparatus for molding foam patterns for use in a lost foam casting process.
A conventional injection molding or die casting apparatus includes a mold piece or die member having therein an aperture and including a surface at least partially defining a mold cavity. The apparatus also includes an ejector pin which has an outer end surface and which is slideably housed in the aperture. The ejector pin is movable between a first or retracted position wherein the outer end surface of the pin is flush with the surface of the mold piece, and a second or extended position wherein the outer end surface of the pin is located outwardly of the mold piece surface so that the ejector pin separates a molded part from the mold piece surface. The mold piece is typically made of an aluminum alloy, and the ejector pin is typically made of a metal that is dissimilar to aluminum, such as stainless steel, chrome-plated steel, brass or copper.
A disadvantage of such an apparatus is undesirable wear on both the ejector pin and the mold piece due to relative movement of the two parts. The pin cannot be lubricated because, at least in the case of apparatus for injection molding foam parts, the apparatus operates in a steamy environment that would remove a lubricant. Also, a lubricant could contaminate a foam part being molded by the apparatus. Furthermore, the breaking of an ejector pin can cause significant damage to the mold piece, and the ejector pin can cause significant damage to the opposite mold piece during a "mold crash," i.e., during accidental closing of the mold pieces with the ejector pin extended.